During the last twelve months a subject which has attracted much attention, is the use of detective or hand cameras; which may be defined as apparatus, by means of which photographs may be taken without the knowledge of the general public. It is in such work as the taking of street views, marine pictures and photographs of rapidly-moving objects, and in the capture of the natural pose and expression of the unconscious human subjects, that the value of the hand camera is felt, as by its unobtrusive appearance, and the absence of all the somewhat tedious usual preparations which too often attract attention and destroy all natural charm, and give rise to that stiffness and self-consciousness which with most people seem to be the natural concomitant of "having their likeness took."
One of the earliest of this class of camera was the Book-shaped Camera," which notwithstanding many later introductions, can still hold its own for simplicity and effectiveness; but now something a little more elaboate has been called for, as the use of this class of camera has been much extended, so as to include general all-round work. It would be impossible within reasonable limits to review in detail the great number which have been introduced to public notice, but a short consideration of the principal features of the various working parts will enable anyone to become at once a better judge of the practical efficiency of any instrument.
The best form is undoubtedly that of the Rapid Euryscope. This working, as it does, at an aperture approximately one-sixth of its focal length, or f/6, renders it invaluable for extremely brief exposures. The next most suitable lens is the Rapid Rectilinear, which works with an effective aperture of f/8; then the Rapid View of the same aperture; and lastly the Wide Angle Euryscope working at f/9.50. It is essential that the lens besides being rapid, should possess that quality called depth of focus, or ability to define upon one plane, objects at varying distances from the lens, and as this quality decreases with an increase of focal length, lenses of comparatively short focus are used.
This should be capable of adjustment from a very rapid to a comparatively slow exposure. The speed at which the shutter should work will depend to a great extent upon the nearness and rapidity of movement of the objects in the field of view - not much assistance can be given on this point, experience alone will enable the worker to decide this.
Many operators assume that the use of a Diaphragm or Stop is not only unnecessary, but an evil when using a shutter at high speed; this, however, is a fallacy Except for dull days and for subjects with very heavy shadows, such as street views, etc, the open aperture of the lens is rarely necessary; very fine work may and can be done with f/10, f/11 and even f/16; for beach or marine work, in brilliant sunshine, the latter is the largest aperture which should be used.
Focussing. Many hand cameras, especially those which have some Automatic plate-changing arrangement, are not fitted with any focussing screen; but we do not think this at all a desirable omission, and would be sufficient for us at least to reject the same, as our idea of the perfection of a hand camera is one which may be used for either work, that is, instantaneous or the ordinary time exposures with a stand. With lenses of short focus, focussing is not an absolute necessity, as there is always a point beyond which everything is sharp when the lens is racked out to its equivalent focus, and this may be easily found by experiment, or the following table will be of assistance, as showing approximately the nearest point in focus, with a doublet lens of given focus and aperture -
With a Rapid View lens of 5in. focus, anything beyond about 15ft. will be in focus with f/10 or f/11, with f/8 about 20ft.
The question as to which of these three appliances is the best is purely a personal equation, as the decision will rest on the purpose for which the camera is desired, and the predilection of the owner; as should he have a penchant for films, then a roller slide will become a necessity. The question as to dark slides or an automatic-changing arrangement will depend to some extent for decision upon the work for which the camera is intended. If for detective or hand work alone, then the absence of a focussing screen, which is the necessary feature of these cameras is not so much felt. And again another advantage of using dark slides is that one is not bound to use one particular brand or rapidity of plate, as many different kinds as holders may thus be tried, and the plate adapted to the special work in hand selected.
No matter what the opinion of some few may be, we consider at least one if not two Finders an absolute necessity, as nothing is more annoying than to make sure that you have included the whole of some particular scene or object upon your sensitive plate, and then to find upon development that, notwithstanding your conviction upon this point, only half or part of the desired object is to be seen. The writer worked for some months without a Finder till, on a particular occasion, the much-desired object was conspicuous by its absence in one, and by being cut in half in another plate, both of which had been fired off on a certain occasion, the like of which would not occur again for twelve months. After that he mounted two Finders. Should any doubt exist as to their function, their usefulness will at once be appreciated when the explanation is given that a Finder shows in miniature, and not reversed, the subject thrown upon the sensitive surface by the lens; thus in the case of photographing any moving object, such as a yacht, the right moment, when the vessel is in the centre of the plate, may be seen, and the exposure made.